This study links two key areas of importance to the prevention of adolescent HIV infection: risky sexual behavior and substance use, incorporating perspectives from both basic and applied science. Active collaborations between these two approaches are rare, although both share assumptions that adolescent problem behaviors are highly correlated; that they share common risk and protective factors; and that they can be reduced by prevention efforts generically aimed at these factors. Nevertheless, long-term effectiveness for most HIV/AIDS prevention programs has not been well established nor have there been conclusive demonstrations of a common etiology underlying covarying problem behaviors of risky sexual activity and substance abuse. This failure to derive theoretically driven and research-based prevention programs is due to the complex nature of theoretical models that address these behavioral domains and to limitations of empirical data previously available. Data from the first two waves of The National Longitudinal Study of Adolescent Health (Add Health) are now available and offer longitudinal data following a large nationally representative sample of adolescents; oversamples of minority and under-served adolescents; and multi-faceted measures at the individual, family, peer, school, and community levels. In the upcoming Wave 111, the results of biological tests for HIV and other sexually transmitted infections will also be available. The proposed study is a collaboration between basic scientists with expertise in adolescent sexuality and prevention scientists with expertise in evaluation of applied adolescent substance abuse prevention programs. A major goal is to understand underlying causes and consequences of patterns of drug use and risky sexual behavior among identified groups of adolescents so that preventive intervention strategies can be developed and appropriately targeted. Specific study aims are: 1) to describe cross-sectional and longitudinal patterns of sex and drug use behavior in adolescence, the persistence of such behavior in young adulthood, and the prevalence of HIV infection in relation to these patterns; 2) to identify individual and contextual factors that can predict patterns of sexual activity and drug use behaviors from adolescence to young adulthood; and 3) to develop recommendations pertaining to the prevention of HIV and drug use risk behavior, The study will use multilevel analyses that incorporate individual and contextual factors to predict behaviors at each cross-sectional time point and to assess behavior longitudinally from adolescence to young adulthood.